Dolby CP750 Digital Cinema Processor Manual - Projectionniste.net

Aligning the Auditorium
5.7.2 Subwoofer Channel Level
Whereas the final sound pressure levels of the main audio channels are ideally adjusted
with a single microphone two‐thirds back from screen at room center, the subwoofer
channel level is best adjusted with the microphone multiplexer cycling (if available).
1. First complete the center channel equalization and level adjustment.
2. On the Channel Tune tab, click LFE to make it the active channel and select Pink
Noise as the Signal Mode.
3. Use the slider and arrow keys to achieve an average level of +10 dB as indicated on the
spectrum analyzer.
This is the “digital” level, which is always set 10 dB higher than the center channel.
4. Click Force PL Cut to activate the Dolby Pro Logic subwoofer and adjust the Cut
slider to achieve an average level of 0 dB as indicated on the spectrum analyzer.
The Pro Logic subwoofer is always set to match the level of the center channel and to
act as bass extension during Pro Logic or Pro Logic II playback.
5.7.3 Subwoofer Speaker Polarity Check
To check subwoofer speaker polarity:
1. Click Center Channel Gen on the Channel Tune tab to generate center‐channel pink
noise.
2. Choose a Filter Frequency to select the crossover point between your main speakers
and the LFE.
Use 50 Hz if your main speakers are full spectrum. Use 100 Hz otherwise.
3. Click Phase Invert and watch the behavior of the filter frequency band. There should
be a level decrease as soon as you click Phase Invert. If you do not see a decrease, the
polarity of the subwoofer wiring is incorrect. Reverse the subwoofer speaker wire
connections to correct it.
The subwoofer polarity always resets to normal after completing this check. Phase
Invert is a temporary setting for this test only.
5.8 Final Sound Check
Follow these steps to do a final equalization check of the auditorium.
1. On the Room Levels tab, click Rotate under Signal Generator Enable.
2. Choose Signal Mode Pink Noise to start pink noise.
Pink noise is sent to each channel in turn, holding for five seconds at each channel.
Note:
Unlike the different levels used during alignment, the rotating pink
noise is set to 85 dB for all channels during this test. Pressing
stops the pink noise from moving to the next channel. Pressing
again resumes pink‐noise rotation.
3. Go to the auditorium and sit two‐thirds of the distance from the front speakers to the
rear, and at the side‐to‐side center of the room. All channels should sound equally
loud and have similar frequency response as the noise rotates. An SPL meter can be
used to confirm accurate and equal level settings.
44 Dolby ® CP750 Digital Cinema Processor Manual